Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$139.39	8.212%	$150.8367	$150.84	$150.85	$150.80
Purchase #2	$95.37	5.508%	$100.623	$100.62	$100.60	$100.60
Purchase #3	$78.90	6.277%	$83.8526	$83.85	$83.85	$83.90
Purchase #4	$26.35	5.495%	$27.7979	$27.80	$27.80	$27.80
Purchase #5	$41.42	4.544%	$43.3021	$43.30	$43.30	$43.30
Purchase #6	$185.75	10.810%	$205.8296	$205.83	$205.85	$205.80
Purchase #7	$247.59	12.856%	$279.4202	$279.42	$279.40	$279.40
7 purchase totals =	$814.77		$891.6621	$891.66	$891.65	$891.60